[ObjC ARC] Converts ios/web/public/test/http_server:http_server to ARC.

ios/web/public/test/http_server/html_response_provider_impl.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/public/test/http_server/html_response_provider_impl.h"
 
 #import "ios/web/public/test/http_server/response_provider.h"
 #include "net/http/http_response_headers.h"
 #include "net/http/http_status_code.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 std::map<GURL, HtmlResponseProviderImpl::Response> BuildResponseMap(
     const std::map<GURL, std::string>& responses_body,
     scoped_refptr<net::HttpResponseHeaders> headers) {
   std::map<GURL, HtmlResponseProviderImpl::Response> responses;
   for (const std::pair<const GURL, std::string>& pair : responses_body) {
     responses.insert(std::make_pair(
         pair.first, HtmlResponseProviderImpl::Response(pair.second, headers)));
   }
   return responses;
@@ skipping 69 matching lines @@
 }
 
 void HtmlResponseProviderImpl::GetResponseHeadersAndBody(
     const web::ResponseProvider::Request& request,
     scoped_refptr<net::HttpResponseHeaders>* headers,
     std::string* response_body) {
   const Response& response = responses_.at(request.url);
   *headers = response.headers;
   *response_body = response.body;
 }